Aircraft engines typically include turbomachinery that is configured for low noise and one or more combustors configured for low nitrogen oxides NOx (e.g., NO and NO2) emissions and operability. The relative contribution of acoustic tones from the combustor to overall noise increases as the contribution of other noise sources is reduced. Reduction in tone amplitude has been demonstrated by creation of local circumferential zones where fuel-air ratio varies. The zones have varying delay times that are observed prior to a release of heat, and consequently, a different coupling to naturally occurring acoustic frequencies.